There is something about the stifling, airless heat of St Louis that induces a headache...and no one knows that more than Jurgen Klopp.

Liverpool's pre-season tour of the States came to a stuttering close here in Missouri, when some serious defensive problems were exposed with the season less than 12 days away.

The Reds boss has signed seven players since he arrived, and all of them have had some influence on his new look side...but it is the old problem that remains, with his team twice gifting goals to Roma.

Former Manchester City striker Edin Dzeko celebrates with his Roma teammates after scoring against Liverpool (Image: Getty Images)

More importantly though, Klopp has just two fit senior centre halves, and no cover at full back, despite spending much of the summer searching for ones on either flank.

He has indicated that James Milner may be employed at left back rather than signing Ben Chilwell, who has been a target for six months or more.

And it seems that Milner had better get used to it, because last season's first choice Alberto Moreno limped off here with a hamstring problem that could make him a doubt for the start of the campaign.

It seems almost incredulous that a club with the latest tv millions – and one who may even make a profit in this summer's transfer market – could go into the campaign with a midfielder at full back, and yet that is the prospect.

Those defensive problems, and the goals that they offered up to Roma's Edin Dzeko – showing his City quality to score through Dejan Lovren's legs – and one time Liverpool target Mohamed Salah, who punished slack marking, overshadowed more promising features for Klopp.

For a start, he has quality in attack, and options to back it up, as youngster Sheyi Ojo showed with a goal just before the interval.

But that headache still persists, and here, our reporter David Maddock offers five observations from St Louis on what the manager must address between now and the start of the new Premier League campaign.

1. Attack stacked

Liverpool have plenty of firepower this season (Image: Liverpool FC via Getty)

Liverpool may have struggled for fluency on their pre-season tour, and still have problems converting the many chances they've created, but they have finally got some real depth in their attacking options.

Even in the season of Suarez and Sturridge and 100 goals, they had no back up, but on this tour they have six strikers who all know where the net is, and a host of talent who can play behind.

2. Is Dan the man?

Is Daniel Sturridge the number one choice for Jurgen Klopp up front? (Image: Liverpool FC via Getty)

Which may be bad news for Daniel Sturridge.

Jurgen Klopp's preference is for one striker up and one behind or wide, with two attacking midfielders in support, so there is room for one centre forward only.

Currently, the manager seems to prefer Divock Origi in that role and Roberto Firmino as back up, while Mane, Wijnaldum, Coutinho, Lallana and Ojo provide the width.

Sturridge started here and had two fine efforts, but he may have to do more to claim a starting place come the season.

3. Negative balance.

Liverpool miss a chance (Image: Liverpool FC via Getty)

If Liverpool do have an impressive array of attacking talent – even forgetting super-Mario – then the fear is they have less depth in other areas.

True, they have injuries at centre half, with three out, but that means they will go into the season with only two fit central defenders.

The same problems arise at full back, with a kid and a midfielder providing back up.

Indeed, James Milner is likely to start ahead of Albert Moreno, who was injured here and could even miss the start of the season.

A whole summer without signing a full back (an obvious area of weakness) sounds like carelessness.

4. Jeepers keepers

Roma defenders call for offside (Image: Liverpool FC via Getty)

Goalkeeper is also an area of concern still, because while the Reds at least have some proper cover (instead of the unfortunate Adam Bogdan), they don't yet seem to have a natural number one.

Both Manninger and Mignolet made good saves here, and both are solid, but it seems Loris Karius is the first choice.

Only trouble is he's injured, AND unused to the Premier League...so unless he steps up on his return, it could still be a slight weakness.

5. Out and about

Plenty of squad players such as Balotelli look like leaving the club (Image: Liverpool FC via Getty)

While there are still some areas that need addressing, and a long way to go to become a complete unit, the biggest headache facing Klopp is the players he doesn't want, not the ones he still requires.

The likes of Balotelli, Benteke, Markovic, Alberto, Wisdom and even perhaps Mama Sakho are all surplus to requirements, but still clinging onto their places (and salaries, no doubt).

For the sake of squad cohesion, he needs to get them out, and as quickly as possible, because so many unsettled players can only have a negative effect.